Numerical control apparatuses (CNC) or programmable controllers connected thereto (PC) have become more sophisticated and complicated due to advances in a semiconductor technology including a microprocessor and a software technology. The malfunction rate of these numerical control apparatuses and programmable controllers has been reduced to a very low level by improvements in reliability technologies, but once a malfunction occurs, it is sometimes difficult to find the portion at which the malfunction exists. More specifically, an overall knowledge of electronics, software, machine tools, machining technologies and the like is required to find the malfunctioning portion.
A malfunction diagnosis system has been proposed wherein a host computer is installed at a service station and a malfunction of a CNC system is diagnosed by connecting the host computer to the CNC system through a communication line instead of dispatching a service engineer to the site at which the CNC system is installed, to diagnose the malfunction.
Nevertheless, even if the portion of the CNC system at which a malfunction has occurred is found as a result of the malfunction diagnosis effected by the host computer connected to the CNC system, a service engineer must be dispatched to the field to repair the malfunction, and it is not always possible to meet the user's request for an immediate dispatch of a service engineer.
On the other hand, as a result of the diagnosis, it is often found that the CNC system is suffering only a local malfunction, and can be returned to use by a suitable processing of the malfunction. Further, it is sometimes found that the CNC system itself has malfunctioned and it is a sequence program or the like that is defective. Therefore, there are many cases wherein a machining operation can be resumed by taking suitable measures, without the need for a service engineer at the site.